ECOS Guide to the Ecology of the Northern Rockies

Native grasslands make up much of the dry, low elevation foothills below the montane zone of the Rocky Mountains including low elevation valleys where most cities and towns are located. The vegetation is adapted to long periods of drought, wide variation in temperature, and periodic grazing by ungulates such as deer and elk in the winter and early spring. Many seed eating birds frequent these habitats as well. Grasslands are home to deep, fertile soils and low-growing plants. This type of community was historically perpetuated by fire and grazing, both of which decreased the abundance of woody plants. Fire does not play as large a role in grasslands as it used to, as fire has been suppressed for approximately 100 years in many places. Grazing does still occur. While animals such as mule deer, and elk graze on plants above, microinvertebrates in the soil below consume as much as four times the amount both above and underneath the ground. The dominant grasses include wheatgrasses, especially bluebunch (Agropyron spicatum), rough fescue (Festuca scabrella), and Idaho fescue (Festuca idahoensis). In addition to grasses, there is a surprising amount of herbaceous plant diversity in native grasslands. Among them, arrowleaf balsamroot (Balsamorhiza saggitata), penstemon species (Penstemon spp.), fleabanes (Erigeron spp.), lupines (Lupinus spp.) and pussy toes (Antennaria spp.) grow interspersed with grasses. Today, urban sprawl, agriculture, and grazing by cattle or sheep threaten native grasslands. Associated with these human impacts is the incursion of exotic plants. These are aggressive invaders, such as spotted knapweed (Centaurea maculosa), cheatgrass (Bromus tectorum), dalmation toadflax (Linaria dalmatica), and leafy spurge (Euphorbia esula). Invaded grasslands generally have poorer habitat values for both wildlife and domestic animals.

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Thickets cover ecotones between forest and grassland in high elevation slopes, north-facing slopes, or in rocky moist areas such as below rock outcrops, in gullies and ravines. They are more moist than grassland habitats, and favor mesic species such as serviceberry (Amelanchier alnifolia), Rocky Mountain maple (Acer glabrum), chokecherry (Prunus virginiana), ninebark (Physocarpus malvaceus), and shiny-leaf spirea (Spiraea betulifolia). An understory of grasses and forbs is common in the more mesic shrublands, including species such as elk sedge (Carex geyeri), fescues (Festuca), and arnica species. Watch out for poison ivy at the edge of moist gullies!

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These harsh semi-arid habitats occur across a broad range of  elevations usually with coarse rocky soils, but can also occur on deeper soils.  Big Sagebrush (Artemesia tridentata.) is dominant with rabbitbrush (Chrysothamnus nauseosus), bitterbrush (Purshia tridentata), and juniper (Juniperus spp.). Grasses such as wheatgrass (Agropyron) and gramma (Bouteloua) species cover the ground below the shrub cover in xeric sites.  These habitats are characterized by wide variation in temperature and dry soils, with the majority of the precipitation falling as snow. Following fire these habitats can be dominated by grasses, but return to sagebrush within a few years. Much of the historic sagebrush habitat has been highly modified within the Missoula valleys.

Thickets often form in an ecotone between grassland and forest.  Near middle summit of MountSentinel, 4900’.  (Photo P. Alaback).

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Low elevation ponderosa pine forest near floodplain of Clark Fork River, Council Grove state park, near Missoula.   (Photo P. Alaback).

Ponderosa pine forests are one of the driest forest types, making up the lowermost part of the montane zone. They are found upslope of the grassy shrublands, and below the Douglas-fir forest. These forests are often made up of open stands of ponderosa pine with a grassy or sometimes shrubby understory. Rough and Idaho fescues (Festuca scabrella and F. idahoensis), and bluebunch wheatgrass (Agropyron spicatum), are the dominant grasses found in this habitat. Shrubs include antelope bitterbrush (Purshia tridentata), snowberry (Symphoricarpos albus), and ninebark (Physocarpus malvus). Historically, periodic fires maintained these forests. Fires created an open forest structure, because they were concentrated below the canopy, burning only the understory grasses, forbs, and lower tree limbs. Additionally, fires were low in intensity, so most plants were able to germinate or resprout shortly after the fire. Today, fire does not burn through these forests as frequently as it once did. With the exclusion of fire, Douglas-fir becomes the climax species in most of these forest stands.

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Mixed larch-ponderosa pine-Douglas-fir forest in PatteeCanyon recreation area near Missoula.  (Photo P. Alaback).

Douglas-fir is the most common conifer in mid-elevation sites in the Rockies, from about 3500’ to 7,000’. It is often mixed with ponderosa pine, lodgepole, and western larch forests. Douglas-fir is a more shade-tolerant tree than these other trees. On wetter, north-facing slopes, Douglas-fir forests occur at lower elevations and encompass a larger area than they do on sunny, dry south facing slopes of the montane zone. Unlike ponderosa pine, Douglas-fir will regenerate very well in the absence of fire, making undisturbed stands quite dense. Undergrowth is variable in these forests, but typically includes snowberry (Symphoricarpos alba) and ninebark (Physocarpus malvaceous). On dry sites or openings, bunchgrasses can be found, on wet sites by contrast twinflower (Linnaea borealis), maple (Acer glabrum), and huckleberry (Vaccinium caespitosum, V. globulare) can be found.

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Clark Fork River near east Missoula.  (Photo P. Alaback).

The floodplain or riparian zone of a river is the interface between the running water and land, extending to the point where the water reaches the land during periods of high water or flood. In order to understand where the floodplain truly begins and ends, one must look to the vegetation. There is a harmonic give-and-take between the plant life and the fluvial activity in a healthy riparian system. Among its many ecosystem functions, riparian vegetation stabilizes the land at the river’s edge and contributes to water quality. Riparian woodland communities often are dominated by uneven stands of cottonwood (Populus) and willow (Salix) species, with an understory of red osier dogwood (Cornus sericea) currants (Ribes spp.) sedges and grasses. While a consistent shallow water table must be present to meet individual plant requirements, periodic flooding is necessary for community maintenance. Flooding transports sediments, creating new landscape features for plants to colonize downstream. A suite of adaptive traits may be found as a result of this disturbance regime. Mechanical adaptations, such as stem flexibility and specialized cells to hold oxygen, assist riparian plants to endure through the physical strains of flood. Reproductive adaptations, including water-dispersible seeds, vegetative budding, and adventitious roots allow the plants to regenerate. Although riparian areas make up a relatively small percent of cover in the Rocky Mountain West, they are, along with wetlands, one of the most important habitats for wildlife. Birds, fish, insects and mammals depend on productive riparian systems for their survival.

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Wetlands are permanently or semi-permanently covered with water at the ground level. This surface water may arise from flooding of nearby rivers, groundwater discharges, precipitation, agricultural irrigation systems, or other sources. These are very significant components of the landscape, as they function as productive wildlife habitat and aquifer and groundwater recharge sources and often create unique habitats which include rare or threatened species. In order to qualify as wetland, some emergent vegetation must be present that has specific adaptations to inundation or wet soils such as cattails  (Typha latifolia) , sedges (Carex spp.) rushes (family Juncaceae), skunk cabbage (Lysichiton americanum), labrador tea (Ledum latifolium), Sphagnum moss species, or others. These plants are known as hydrophytes. Hydrophytes can survive in standing water or soils that lack oxygen for long periods of time. Wetlands are a key habitat for numerous waterfowl species as well as other birds, such as rails, Ruby-Crowned Kinglets, Song Sparrows, Western Tanagers, and many others. Wetlands are some of the most endangered habitats, declining as a result of human disturbance, such as agriculture, urban development, and water pollution. Even roadbuilding in a watershed that includes a wetland can have a significant influence since it can affect the flow of groundwater and the size or extent of wetland development. Good examples of wetlands can be found along the Bitterroot and Clark Fork River and in several wildlife refuges in the major valley bottom habitats of our area.

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Aquatic habitats may have emergent vegetation, none at all, or submergent plants, found deep below water. When emergent vegetation dominates, the habitat is generally considered a wetland, although when hydrophytes are present along the fringes of an aquatic area that denotes a transition into a wetland. Aquatic vegetation includes algae, floating leafy plants, such as water-lilies (Nuphar sp.), pondweeds (Potamogeton spp.)  and buttercups (Ranunculus aquatilus). Aquatic habitats are valuable to wildlife, including many species of birds, and are important indicators of water quality. They are also critical habitats for many complex aquatic food webs including many kinds of invertebrates, amphibians, and fishes.

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High elevation meadow in Bob Marshall Wilderness (Photo P. Alaback).

Meadows/Wet Meadows

Meadows are generally found near lakes and streams, beneath snow-covered slopes, or nestled among moist forests. Meadows often are capable of supporting forests, but due to short growing seasons, fires or other disturbances are dominated by grasses. They are not quite saturated with water, but soil is often moist, at least in the spring and early summer, with lush grasses and forbs. Plant communities vary depending on slope, aspect, moisture availability, nutrients and elevation. Meadows are distinctive from grasslands due to the inputs from and interactions with the surrounding ecosystems. Species richness or diversity is greatest at the transition zone between the meadow and the forest. Characteristic species can include Calamagrostis  and Poa spp. grasses, fireweeds (Epilobium spp.), sedges (Carex spp.), false hellebore (Veratrum viride), and many composites (e.g. Erigeron spp., Aster spp.).

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Higher elevation slopes with a mix of large rocks and thin soil create harsh habitats for plants. These sites often are quite exposed, leading to high wind and cold temperatures. Cushion plants are often the only plant type found between rocks. These dry habitats, even though they occur in mountains with much higher annual rainfall and less evaporation than lower elevation grasslands often include some of the same species since adaptation primarily involves growing in a moisture-limited environment. Examples include Gaillarida, Lithofragma, and some Arnica and Erigeron species. These plants usually have very small leaves that help to alleviate water loss, and very dense growth habits that help the plant to retain warmth. Alternatively they grow only following snowmelt when there is adequate moisture. Scree or talus is the carpet of rocks often found on very steep slopes. It generally supports small patches of vegetation, and it is very difficult to move across, due to its extreme instability.  Alders and even aspen can often colonize at least the edges of these habitats. Dogbane is common in these habitats as well.

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Disturbed areas include roadsides,  ditches, power lines, construction sites, old fields, and other areas that have been recently affected by humans. These areas often become invaded by exotic species, introduced primarily from Eurasia, such as dandelion, many annual mustards such as shepard’s purse (Capsella), mullein (Verbascum spp.), thistles (Cirsium spp.)  spotted knapweed (Centaurea maculosa), cheatgrass (Bromus tectorum), dalmation toadflax (Linaria dalmatica), and leafy spurge (Euphorbia esula). The extent to which an area is invaded depends on a number of factors, all of which are under considerable scientific debate. One hypothesis is that these plants have no natural predators here, allowing them to displace native species relatively quickly. Another factor is that these species sometimes have novel adaptations that allows them to reproduce better than native species. Others have apparently co-evolved with humans and have developed special adaptations to the habitats that we tend to create, such as roadsides, and abandoned agricultural areas. In most cases exotics tend to be more aggressive in colonizing disturbed habitats than native species, especially immediately after disturbance. Regardless of the reason, aggressive exotic species were purposefully introduced (or accidentally carried) by humans, and are now one of the most contentious ecological issues for conservationists and land managers in the Northern Rocky Mountains. Knowing which weeds are common in a site often gives you a valuable clues as to the human history of a given area.

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Secondary Forest (Burned or Logged)

Intense wildfire or clearcut logging often creates a dense forest that can dominate a site for a century or more. In more moist or high elevation sites lodgepole pine trees are generally the first trees to establish following a large disturbance such as fire, logging or insect attack. Thirty to one hundred years later lodgepole stands often are dense and dark, creating a forest that has little understory diversity. Knickinick (Arctostaphylos uva-ursi) is a particularly common species in these forests. Older stands may become more open over time, providing opportunities for understory trees to grow, such as Engelmann spruce and subalpine fir. Lodgepole stands are highly susceptible to fire. They are often made up of several ages of trees. As trees die and fall, logs accumulate, fueling “log-to-log” fires throughout the understory, and scarring trees, continuing the fire cycle. Dense secondary forests also occur in moist fertile sites with little understory shrub and herb diversity. This is particularly common in grand fir forests, and western hemlock in northwestern Montana and adjacent Idaho, but can occur in productive Douglas-fir forests as well. In these forests understory plants often include fern species, and small herbs or shrubs such as Oregon grape (Berberis spp.), Pyrola spp. and Vaccinium species.

Douglas-fir forest two years after the large wildfires in Yellowstone National Park. This lush grassy understory will eventually give way to a more sparse understory as a new dense forest develops in the wake of the old burned forest.

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Timberline along limestone bluffs in the Rocky Mountain Front on the eastern slope of the Rockies south of Glacier National Park.  (Photo P. Alaback)

Subalpine forest/Subalpine-fir/Spruce

Subalpine fir and Englemann spruce are the primary conifer species found in the forest below the alpine zone. Subalpine fir eventually becomes the dominant species if there are no subsequent disturbances. At the lowest extent of these forests, Douglas-fir may be present. At higher elevations whitebark  pine (Pinus albicaulis) and alpine larch (Larix lyallii) may also be present, but usually in more open woodland like patchy forest. At the highest extent, stunted and gnarled trees named “krummholz” hold their ground, and form small patches of forest. These twisted trees, usually subalpine fir, mark the highest point in which trees can grow, as there is insufficient energy (or growing season length) to sustain an upright woody lifeform.  Krummholz grow close to the ground, where air is warmer and wind is milder. The growing season is very short in the subalpine zone, and snow may remain until July. Regardless, some of the most stunning wildflower shows occur here if  you are there at the right time. Among the low growing, showy herbs are columbines (Aquilegia sp.), anemones (Anemone sp.), and glacier lilies (Erythronium grandiflorum). Alpine and rocky alpine habitats are often interspersed with subalpine forest near timberline (compare with descriptions in those sections).

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Habitat References

Agee, J.K. (1993) Fire Ecology of Pacific Northwest Forests. Island Press. Washington, D.C. and Covelo, CA.

Cordes, L. D.; Hughs, F.M.R.; Getty, M. (1997) Factors Affecting the Regeneration and Distribution of Riparian Woodlands Along a Northern Prairie River: The Red Deer River, Alberta. Canada Journal of Biogeography. 24:5. 675-695.

Hansen, P. L., R. D. Pfister, K. Boggs, B. J. Cook, J. Joy and D. K. Hinckley. 1995. Classification and management of Montana's riparian and wetland sites. Montana Forest and Conservation Exp. Sta., School of Forestry, University of Montana, Missoula, MT 54. pp.

Kershaw, L.; MacKinnon, A.; and Pojar, J. (1998) Plants of the Rocky Mountains. Lone Pine Publishing.Canada.

Mueggler, W. F. and W. L. Stewart. 1980. Grassland and shrubland habitat types of western Montana. USDA Forest Service, Intermountain Res. Station INT-66 154pp. Ogden, UT.

Naiman, R.J. and Decamps, H. (1997) The Ecology of Interfaces: Riparian Zones.
Annual Review of Ecology and Systematics. 621-658.

Pfister, R. D., B. L. Kovalchik, S. F. Arno and R. C. Presby. 1977. Forest Habitat Types of Montana. USDA Forest Service, Intermountain Forest and Range Experiment Station INT-34. Odgen, UT..

Schultz, J. (1995) The Ecozones of the World: The ecological divisions of the geosphere. Springer-Verlag. Berlin, Heidelberg, New York.

Scott, G.A.J. (1995) Canada’s Vegetation. A World Perspective. McGill-Queen’s University Press. Montreal & Kingston, London, Buffalo.

Websites:

Wyoming Partners in Flight. Wyoming Bird Conservation Plan.

http://www.blm.gov/wildlife/plan/WY/Wyoming%20Bird%20Conservation%20Plan.htm#table_of_contents. Viewed on March 31, 2005.

Contributors:  Lauren Preistman, Paul Alaback

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